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Investigation of optical nonlinearities in InN layers by using time-resolved differential transmission and light-induced transient grating techniques

Saulius Nargelas 1T. Malinauskas 1Arunas Kadys 1Mikas Vengris 2Kestutis Jarasiunas 1Emmanouil Dimakis 3Theodore Moustakas 3

1. Vilnius University, Institute of Materials Science and Applied Research, Sauletekio ave. 9-3, Vilnius LT-10222, Lithuania
2. Vilnius University, Laser Research Center, Sauletekio Ave. 10, Vilnius LT-10223, Lithuania
3. Boston University, Department of Electrical and Computer Engineering, Boston, MA 02215, United States


Picosecond dynamics of light induced optical nonlinearities was investigated in InN layers over wide range of temperature and excitation using complementary time-resolved pump-probe techniques. Picosecond light-induced transient grating (LITG) technique has been applied for investigation of nonequilibrium carrier diffusion and recombination in T=15K-300K range. Femtosecond differential transmission (DT) technique provided kinetics of induced bleaching and free carrier absorption in 1550-2300 nm spectral range. The measurement were carried out in two (2.3 μm and 0.6 μm thick) InN layers grown on sapphire with background electron density of 1.4×1018 cm-3 and 4.7×1018 cm-3.
LITG experiments provided novel features of non-equilibrium carrier recombination in highly excited InN (Δn>1018 cm-3). The recombination rate was found strongly nonlinear and followed the dependence 1/τR∝B*(n0+N) which was nearly independent on temperature down to 40K. These features allowed us to suggest a trap-assisted Auger recombination being the dominant recombination mechanism in InN. The modelling provided a value of trap-assisted Auger recombination coefficient B*=8×10-10 cm3s-1.
DT kinetics at fixed pump energy and various probe wavelengths revealed the spectral range, where the induced bleaching was dominating (for wavelengths above the absorption edge at ~0.7eV). By increasing probe wavelength, we observed a gradual transfer from the optical bleaching (Δα<0) to the induced free carrier absorption (Δα>0 at λp>2260 nm) as well as the intermediate spectral region when these DT effects nearly cancelled each other. Measurements of free carrier absorption kinetics and determined carrier lifetimes at various excitation energy densities confirmed the inverse dependence of lifetime vs total carrier density. Moreover, the latter data provided a value of B*=4×10-10 cm3s-1, which is close to the one obtained by LITG technique.


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Presentation: Poster at E-MRS Fall Meeting 2009, Symposium A, by Saulius Nargelas
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-25 17:20
Revised:   2009-06-07 00:48